View Single Post
Old 9th May 2011, 1:36 pm   #7
ENGLISH VICTOR
Hexode
 
Join Date: Feb 2008
Location: Sydney, Australia
Posts: 356
Default Re: Bush TV12 Poor Contrast

The TV11 and 12 had remarkably high gain, bandwidth, and stability, the fact that the contrast only needs to be backed off a little for both sound and vision to dissapear points to the first two R.F.stages V11 and V12. With the contrast control set for maximum gain measure the cathode voltages of the two valves mentioned, they should be on the order of 1.5 Volts and check that the anode voltages are about 190V, the screen voltages should be exactly the same as their respective anode voltages.
If all seems in order check the alignment again following the alignment procedure exactly as per Bush instructions. The Aurora as mentioned should drive the set crazy with severe vision on sound and visa versa with the contrast set to maximum.Finaly check the cathode and screen/anode decoupling caps. The valve holders I have been told can cause similar problems when they become corroded. Low cathode voltages indicate a low emission valve but only with the contrast control set for maximum gain.
Good luck.
Victor.
ENGLISH VICTOR is offline